Waveguide structure utilizing compliant continuous support

ABSTRACT

A waveguide structure is formed by supporting a waveguide section within a section of conduit by a low modulus continuous support material such as oil extended rubber which fills the space between the waveguide and conduit. This continuous support material eliminates distortions from weight loading induced deflections and provides substantial corrosion protection to the waveguide.

United States Patent [1 1 Kaufman et a1.

WAVEGUIDE STRUCTURE UTILIZING COMPLIANT CONTINUOUS SUPPORT [75]Inventors: Stanley Kaufman, Flanders; Milton Lutchanslty, Randolph Twp.,Morris County; Raffaele Antonio Sabia, Lincroft, all of NJ.

[73] Assignee: Bell Telephone Laboratories Incorporated, Murray Hill,NJ.

[22] Filed: Dec. 15, 1971 [21] Appl. No.: 208,207

[52] US. Cl. 333/95 R, 333/98 R, 333/98 M, 174/98, 260/33.6 A [51] Int.Cl. 1101p 1/00, 1101p 1/30, 1101p 3/12 [58] Field-of Search 0333/98 R,95 R, 95, 333/98; 174/98; 260/36.6 A0, 77.5 AT

[56], 5 References Cited.

UNITED STATES PATENTS 3,605,046 9/1971 Miller 333/98 RX 3,434,994 3/1969Smitet a1. 260/29.7 GP

366,174 7/1887' Kruesi "174/29 X 3,359,351 12/1967 Bender.. 139/149 X'327,477 9/1885 'Spalding 174/98 1,959,368 5/1934 Kennedye 138/112 X2,764,565 9/1956 Hoppe et a1... 260/2.5 AC 2,848,696 8/1958 Miller333/95 R 2,966,643 12/1960 Kohman et a1... 333/95 R 3,007,122 10/1961Geyling 333/95 R 3,108,980 10/1963 Gwin et a1 260/33.6 AQ

[ July 24, 1973 3,121,206 2/1964 Mandel 333/ R 3,246,073 4/1966 Boucheet a1... 174/42 3,345,245 10/1967 l-lanusa 138/111 X 3,479,621 11/1969Martin 333/95 R 3,492,607 1/1970 Effemey 333/95 R OTHER PUBLICATIONSVerdol et al., Liquid Castabl e Elastomers from l-lydroxl-TerminatedPolybutadienes, Parts 1 AND 11, Rubber Age, July & Aug. 1966, pp. 57-64,62-68 Albersheim, W. J., Propagation of TE Waves in Curved Wave Guides,B.S.T.J., V01. 28, 1-1949, pp. 26-32 Unger, H. 3., Circular ElectricWave Transmission Through Serpintine Bends, B.S.T.J., V01. 36, 9-1957,pp. 1279-1291 Primary Examiner-Rudo1ph V. Rolinec Assistant Examiner-Wm.H. Punter Attorney-W. L. Keefauver and Edwin E. Cave [57] ABSTRACT Awaveguide structure is formed by supporting a waveguide section within asection of conduit by a low modulus continuous support material such asoil extended rubber which fills the space between the waveguide andconduit. This continuous support material eliminates distortions fromweight loading induced deflections and provides substantial corrosionprotection to the waveguide.

5 Claims, 2 Drawing Figures PATENIEDJuL24|91a FIG. 2

SUPPLY FIG.

WAVEGUIDE STRUCTURE UTILIZING COMPLIANT CONTINUOUS SUPPORT BACKGROUND OFTHE INVENTION 1. Field of the Invention This invention relates towaveguide transmission systems and more particularly to a waveguidestructure having a compliant continuous support for supporting thewaveguide within a conduit, isolating it from disturbances in thesurrounding environment and eliminating weight loading induceddeflections and deflections due I to axial forces in the waveguide.

2. Description of the Prior Art The ever increasing demand forcommunications facilities is producing an increasing interest in the useof waveguide transmission lines as extremely broad frequency band longdistance transmission media. One requirement for such a waveguidetransmission system is that the waveguide tube be isolated fromdisturbances in the surrounding environment because the performance ofthe waveguide is critically dependent upon the maintenance of a highdegree of straightness of the waveguide tubes. Thus, buried waveguide inparticular must be isolated from disturbances in the surroundingenvironment such as irregularities in the trench bottom as well as earthtremors, vibrations, and faultings.

A limited degree of isolation may be achieved by simply enclosing thewaveguide in a relatively large diameter conduit. When disturbances inthe surrounding environment distort the conduit, the waveguide can moveaway from the conduit walls and thereby maintain its straightness.

A waveguide structure having an improved waveguide support system isdisclosed in U.S. Pat. No. 3,007,122 issued to F. T. Geyling on Oct. 31,1961. This patent teaches mounting the waveguide on fluid filledflexible members or bellows which are interconnected by a feeder tubeand supported within a protective conduit.

Another waveguide structure having a support system utilizing a pulleyand interconnecting cord arrangement is disclosed in US. Pat. No.3,609,603 issued to M. Lutchansky on Sept. 28, 1971, and assigned to theassignee of this application.

Still another waveguide structure having a support system which placesthe waveguide under tension within the conduit thereby to maintain thestraightness is shown in 'U.S. Pat. No. 3,605,046 issued to S. E. Milleron Sept. 14, 1971., and assigned to the assignee of this application.

Despite the substantial improvements disclosed in the foregoingwaveguide structures, the support systems of these structures remainmore complex than desired for a system which must be quickly andeconomically installed underground.

The result of distortions or deflections which occur in presently knownwaveguide structures is to produce electrical loss through modeconversion. Significant distortions can be produced by weight loadingand by the large lateral loads that occur in a route bend due tothermally induced axial tensions when expansion joints are not used inthe system. Such deflections occur between the discrete support pointsutilized in the previously disclosed support systems.

SUMMARY OF THE INVENTION The foregoing problems are solved in accordancewith the principles of the invention by utilizing a waveguide 'structurein which the waveguide is supported within a conduit by a low moduluscontinuous support material such as an oil extended rubber. Thewaveguide is centered in the conduit and a suitable composition ofmaterial is poured into the conduit completely surrounding thewaveguide. The material is then cured in place thereby providing acontinuous low modulus support for the waveguide. The material preventsmoisture and other corrosion producing forces from reaching thewaveguide in the event of a failure in the conduit. The low modulusmaterial isolates the waveguide from disturbances in the surroundingenvironment and eliminates weight and thermal loading induceddeflections because of the continuous nature of the support.

DESCRIPTION OF THE DRAWING The invention will be more fully comprehendedfrom the following detailed description and accompanying drawing inwhich:

FIG. 1 is a longitudinal sectional view of a waveguide structure made inaccordance with the invention; and

FIG. 2 is a sectional schematic representation of a method forfabricating the structure of FIG. 1. The same numbers are usedthroughout to refer to similar elements.

DETAILED DESCRIPTION FIG. 1 shows a sectional view of a waveguidestructure 101 comprising a waveguide 2supported within a surroundingprotective conduit 4. Waveguide 2 can comprise any of the various wellknown types of waveguide including helix waveguide, dielectric-linedwaveguide, etc., each of which types normally includes a metal tube asits outer jacket. Conduit 4 is substantially larger than waveguide 2.Conduit 4 can comprise a tube of metal such as steel, plastic such aspolyvinyl chloride (PVC) or cement-asbestos or the like. Structure 101is joined with like structures by known coupling apparatus to fonn along distance transmission line. That is, waveguide 2 is joined on itsends 1 and 3 to respective ends of adjacent waveguide sections andlikewise conduit 4 is joined on its ends 5 and 7 to the respective endsof adjacent conduit sections. When connecting waveguide structures 10!to form a continuous line, it is normally necessary to have access tothe respective ends 1 and 3 of waveguide 2. Since no substantialrelative motion of conduit 4 with respect to waveguide 2 can be obtainedas will become apparent subsequently, it is desirable to have ends 1 and3 of waveguide 2 extend beyond the ends 5 and 7, respectively, ofconduit 4 a distance sufficient to allow working room for connectingends I and 3 with the adjacent waveguide. After the waveguide ends areconnected a short conduit coupling section can be installed to bridgebetween the recessed ends of the adjacent conduit sections 4. Thisconduit coupling section can be filled with material 6 if its length issignificant or if otherwise desired.

Conduit 4 may be deformed by disturbances in the surroundingenvironment. Thus waveguide 2 must be supported within conduit 4 in sucha manner as to be isolated from these deformations. Additionally, thedeflections or deformations of waveguide 2 because of its own weightloading and lateral loading caused by the effects of temperature changesmust be held to a minimum. A support providing isolation and eliminatingweight loading and temperature change induced deflections is obtained byusing a very low modulus continuous support material 6 to surround andsupport waveguide 2 within conduit 4. The low modulus material 6 permitsthe axis of conduit 4 to readily deform with respect to the axis ofwaveguide 2 without transmitting a significant portion of the deformingforces to waveguide 2. The continuous support provided by material 6eliminates weight loading induced deflections by eliminating discretesupport points between which such deflections can occur.

Material 6 advantageously can be in a liquid form initiallyto permit themanufacture of waveguide structures as discrete units as illustrated inFIG. 2. A waveguide 2 is placed within a conduit 4 and substantiallycentered therein about the longitudinal center line 24. This isaccomplished by inserting the ends of waveguide2 into concentric flanges16 on caps 14 which fit over the ends of conduit 4. Caps 14 seal theends of conduit 4. An appropriate low modulus material 6 in liquid formis pumped from a source 22 via pipe 20 through an opening 18 in one cap14 into the space between waveguide 2 and conduit 4. An opening 17 isprovided in the top cap 14 to permit the escape of gasses during thefilling operation. The material 6 is then allowed to cure in placeforming the low modulus continuous support previously discussed. Caps 14are then removed. In order to eliminate weight loading distortions inthe waveguide, the assembly shown in FIG. 2 must be vertical. Tofabricate long sections it may be desirable to utilize a horizontalprocess. In this case it is necessary to center the waveguide within theconduit with a compliant virtually continuous initial support thatallows the filling of the conduit while not permitting distortions dueto weight loading. The initial support will be encased in the lowmodulus material and the effective modulus of the combination will besomewhat higher than the modulus of either constituent support actingindependently. An initial support which could'be utilized for thispurpose is a length of compliant tubing wrapped in the form of a helixaround the waveguide as described in the copending application of J. C.Bankert et al., Ser. No. 205,796, filed 12-8-71 and assigned to theassignee of this application. It is apparent that waveguide structure101 can be mass fabricated in a factory and shipped as a unit to thefield where it can be quickly installed.

The most important property of material 6 is its foundation modulus orequivalent spring constant per unit length of waveguide 2. Material 6eliminates deflections due to the weight loading of waveguide 2 byproviding a continuous support along waveguide 2. However, deformationsof conduit 4 must be isolated or filtered to prevent resultingdeflections in waveguide 2. In particular deformations of conduit 4having mechanical wavelengths corresponding to the beat wavelengthsbetween the primary wave mode being transmitted and degenerate orspurious modes must be filtered. The mechanical wavelengths which aremost important at a given operating frequency increase in proportion tothe square of the inside diameter of waveguide 2. A material having anequivalent spring constant of no greater than 30 pounds per inch ofcompression of material 6 per inch of length of waveguide 2 willsufficiently filter or isolate most deformations having mechanicalwavelengths of interest from waveguide of sizes presently deemedpractical. On the other hand, a foundation modulus of pounds per inch ofcompression per inch of length is a practical lower bound for limitingthe radial deflection of the curved sections of waveguide sufficientlyto avoid contact with the protective jacket when the waveguide issubjected to thermal stresses. For example, with material 6 having anequivalent spring constant within the above stated range of 10 to 30pounds per inch of compression per inch of length,

the losses in a 2 inch inner diameter waveguide enclosed is a steelconduit 4 resulting from deformations of conduit 4 should be no greaterthan 0.1 db per mile if reasonable manufacturing and installationmethods are followed.

The foundation modulus can be lowered for a given material compositionby increasing the diameter of conduit 4. The manner in which thefoundation modulus varies with the material and geometric parameters isgiven approximately by the following formula where k is the formulationmodulus in pounds per inch of compression per inch of length, E isYoung's modulus in pounds per square inch, 1/ is Poisson's ratio, and r,and r refer to the inner and outer radii or material 6, respectively.This formula was derived from results presented by W. A. Gross in anarticle entitled The Second Fundamental Problem of Elasticity Applied toa Circular Ring in Zeitschrift fuer Angewandte Mathematik und Physik(ZAMP), Vol. III, pp. 71-73, 1957.

The creep properties of material 6 must be such that the increase indeflection under sustained load will not exceed 50 percent of theinitial deflection from that load over an expected life of approximately40 years.

In addition to the foundation modulus and creep requirements discussedabove, material 6 must also meet other requirements. For example, itmust be compatible with waveguide 2 which typically has a steel outerjacket and conduit 4 which may be steel, polyvinyl chloride, etc.Material 6 must be resistant to attack from agents such as water, oil,micro-organisms, vermin, etc., which can access material 6 is failuresoccur in conduit 4. Material 6 should have high electrical resistivity,and good tear resistant properties. The proper ties of material 6 mustremain stable with time, temperature, and the stresses placed thereonbecause of deformations in conduit 4. Since material 6 advantageously isin a liquid form initially, the formulation of material 6 should be suchthat it cures in place at room temperature to provide the low modulussupport. Room temperature curing minimizes shrinkage and therebyminimizes stresses resulting from shrinkage.

One material having the foregoing properties is a highly extended orplasticized rubber. Thus a suitable rubber plasticized with a compatiblediluent such as a solvent oil can be used for material 6. Rubbers whichcan be used include the rubbers containing unsaturation such as naturalrubber, styrene butadiene rubber, ethylene propylene diene rubber aswell as rubbers often used in casting compounds such as silicons,epoxies, and urethanes. Urethane rubbers are preferable andpolybutadiene based urethanes are the most preferable. Plasticizers ordiluents which can be used include aromatic and aliphatic petroleumoils, dioctal pthalate or other aromatic esters with the aromatic typepetroleum oil or plasticizers being required when etc., can also beadded to the composition as desired.

Typical composition for material 6 will contain between 5 and percentrubber and 85 to 95 percent diluent.

One example of a plasticized polyurethane rubber is a 7 percent rubbercomposition, i.e., containing approximately 7 percent rubber polymer inthe final formulation, formed from a solution comprising: 50 grams perliter of solution of hydroxyl terminated liquid polybutadiene having ahydroxyl functionality between 2.2 and 2.4 and a hydroxyl contentbetween 0.75 and 0.90 equivalents per kilogram, such as that availableunder the trademark R-45 HT Poly bd from ARCO Chemical Company as therubber polymer; grams per liter of solution of MDl (diphenylmethanediisocyanate) prepolymer of R-45 HT Poly bd hydroxyl terminated liquidpolybutadiene containing 8 to 10 percent isocyanate (NCO) as thecrosslinking rubber polymer; 20 milliliters per liter of solution ofdibutyl tin dilaurate such as that available under the trademarkCatalyst T-lZ from M&T Chemicals, lnc., as the catalyst; and anaromaticpetroleum oil containing more than 90 weight percent of aromaticmolecules, such as that available under the trademark Kenplast G fromKenrich Petrochemicals, lnc., in which the above components are alldissolved. The foregoing solution cures at room temperature to form alow modulus composition. When utilized to support a waveguide having anouter diameter of approximately 2.3 inches in a conduit having an innerdiameter of approximately 4.25 inches, the above composition provides acontinuous support having a foundation modulus of approximately 20pounds per square inch. The same material provides foundation modulus ofapproximately 12 pounds per square inch if the conduit inner diameter isincreased to 5.0 inches.

Another example of a plasticized polyurethane rubber is a compositioncontaining approximately 7.7 percent rubber polymer in the finalformulation formed from a solution comprising: 55 grams per liter ofR-45 HT Poly bd hydroxyl terminated liquid polybutadiene; 22 grams perliter of the MD] prepolymer of the liquid polybutadiene; 20 millilitersper liter of Catalyst T-l2 dibutyl tin dilaurate; and Kenplast Gplasticizing solvent oil. This composition provides a material having afoundation modulus of approximately 20 pounds per square inch when usedto support a waveguide having an outer diameter of approximately 2.3inches in a conduit having an inner diameter of approximately 5.0inches. In the two foregoing examples, the amounts of the hydroxylterminated polybutadiene can be varied between 50 and 60 grams per literand the amounts of the MDl prepolymer of the polybutadiene can be variedbetween 20 and 25 grams per liter.

Another example is a seven percent rubber composition formed from asolution comprising: 70 grams per liter of R-45 HT Poly bd hydroxylterminated liquid polybutadiene; 8.5 grams per liter of isocyanate (MDI)65 from The Upjohn Company as the crosslinking agent; 10 milliliters perliter of stannous oleate such as that available under the trademarkCatalyst T-6 from M&T Chemicals, lnc., as the catalyst; and Kenplast Gplasticizing solvent oil. This composition provides amaterial having afoundation modulus of approximately 10 pounds per square inch when usedto support a waveguide having an outer diameter of approximately 2.3inches in a conduit having an inner diameter of approximately 5.0inches.

Still another example is an eight percent rubber composition formed froma solution comprising-80 grams per liter of R-45 HT Poly bd hydroxylterminated-polybutadiene; 9.75 grams per liter of lsonate l43L MDI; l0milliliters per liter of Catalyst T-6 stannous oleate; and Kenplast Gplasticizing solvent oil. This composi tion provides a material havingafoundation modulus of approximately 30 pounds per square inch when usedto support a waveguide having an outer diameter of approximately 2.3inches in a conduit having an inner diameter of approximately 5.0inches. In the two'foregoing examples, the amounts of the isocyanate canbe varied between 8 and 10 grams per liter. ii

In the foregoing examples, the aromatic oil used is available asmentioned from Kenrich Petrochemicals, lnc., under the trademarkKenplast G. Its main properites are:

Specific gravity 1.02

Viscosity at 25 C. l l cps Pour point of F. 40

Mixed analine point F. 60

Flash point F. 290

Hydrocarbon analysis,wt (Clay-Gel analysis) Polar resins 4 Aromatics 95Saturates l A high flash point is desirable from safety considerations.

The polybutadiene used is a hydroxyl terminated liquid polybutadieneobtainable under the trademark R- HT Poly-bd from the ARCO ChemicalCompany. Its main properties are:

Polybutadicne isomer content:

Trans l, 4

Cis l, 4 20% Vinyl l 2 20% Viscosity at F. poise Moisture wt 0.05

Iodine Number 398 Hydroxyl Content 0.85 equivalents/kgm Although theforegoing discussion primarily has dealt with the use of a low modulussupport material as a distinct support system, the material can also beutilized in conjunction with an initial support system as previouslymentioned. The factory assembled unit could include only the initialsupport system. After installation of such a waveguide unit in theground, a liquid which would cure to a low modulus material inaccordance with this invention could be injected into the conduitsurrounding the waveguide. This material would then provide thecontinuous support necessary to carry the lateral loads associated withtemperature changes as well as provide waterproofing and corrosionprotection as previously discussed. The initial support system providesfor disturbances caused by the initial trench bottom irregularities,etc., and thus the combined support system would need to eliminate onlythe long term disturbances. The somewhat stiffer support resulting fromsuch a combined support system would be acceptable. Although the supportmaterial offers advantages, such as preventing the axial migration ofwater, when it bonds to both the waveguide and conduit, it is notessential that such bonding be obtained to either the conduit or thewaveguide. Without bonding, the material still provides an effective lowmodulus continuous support even though less corrosion protection may beprovided to the waveguide; The equivalent spring constant provided bythe support material will tend to be higher in bonded situations than inunbonded applications.

While the invention has been described in detail with respect tospecific embodiments thereof, it is to be understood that variousmodifications thereto might be made by those skilled in the art withoutdeparting from the spirit and scope of the following claims.

What is claimed is: l. A waveguide structure comprising in combination:a section of waveguide; a section of rigid protective jacket surroundingsaid section of waveguide and spaced therefrom; and an initially lowviscosity liquid material filling the space between said waveguide andsaid jacket and supporting said waveguide within said jacket, saidmaterial comprising a solvent oil gelled by the in situ catalyticreaction of a hydroxyl-terminated polybutadiene with a crosslinkingagent, said hydroxyl-terminated polybutadiene having an averagefunctionality sufficient to form a cross-linked network that gels saidoil, said oil comprising the major fraction by weight of said material,and said material having an equivalent spring constant per inch oflength along said structure of 10 to 30 pounds per inch of compressionof said material. 2. Apparatus in accordance with claim 1 wherein saidsolvent oil is an aromatic solvent oil containing a major proportion ofaromatic molecules; said hydroxylterminated polybutadiene is present inamounts from 50 to 60 grams per liter of said initially liquid material;said crosslinking agent comprises a diphenylmethane diisocyanateprepolymer of said hydroxyl-terminated polybutadiene; and said agent ispresent in amounts from 20 to 25 grams per liter of said material.

3. Apparatus in accordance with claim 2 wherein said hydroxyl-terminatedpolybutadiene has a hydroxyl functionality between 2.2 and 2.4 and ahydroxyl content between 0.75 and 0.90 equivalents per kilogram, andsaid oil contains at least 90 weight percent of aromatic molecules.

4.-Apparatus in accordance with claim 1 wherein said solvent oil is anaromatic solvent oil containing a major proportion of aromaticmolecules; said hydroxylterminated polybutadiene is present in amountsfrom to grams per liter of said initially liquid material; and saidcrosslinking agent comprises isocyanate and is present in amounts from 8to 10 grams per liter of said material.

5. Apparatus in accordance with claim 4 wherein said hydroxyl-terminatedpolybutadiene has a hydroxyl functionality between 2.2 and 2.4 and ahydroxyl content between 0.75 and 0.90 equivalents per kilogram, andsaid oil contains at least weight percent of aromatic molecules.

1. A waveguide structure comprising in combination: a section ofwaveguide; a section of rigid protective jacket surrounding said sectionof waveguide and spaced therefrom; and an initially low viscosity liquidmaterial filling the spaCe between said waveguide and said jacket andsupporting said waveguide within said jacket, said material comprising asolvent oil gelled by the in situ catalytic reaction of ahydroxyl-terminated polybutadiene with a crosslinking agent, saidhydroxyl-terminated polybutadiene having an average functionalitysufficient to form a cross-linked network that gels said oil, said oilcomprising the major fraction by weight of said material, and saidmaterial having an equivalent spring constant per inch of length alongsaid structure of 10 to 30 pounds per inch of compression of saidmaterial.
 2. Apparatus in accordance with claim 1 wherein said solventoil is an aromatic solvent oil containing a major proportion of aromaticmolecules; said hydroxyl-terminated polybutadiene is present in amountsfrom 50 to 60 grams per liter of said initially liquid material; saidcrosslinking agent comprises a diphenylmethane diisocyanate prepolymerof said hydroxyl-terminated polybutadiene; and said agent is present inamounts from 20 to 25 grams per liter of said material.
 3. Apparatus inaccordance with claim 2 wherein said hydroxyl-terminated polybutadienehas a hydroxyl functionality between 2.2 and 2.4 and a hydroxyl contentbetween 0.75 and 0.90 equivalents per kilogram, and said oil contains atleast 90 weight percent of aromatic molecules.
 4. Apparatus inaccordance with claim 1 wherein said solvent oil is an aromatic solventoil containing a major proportion of aromatic molecules; saidhydroxyl-terminated polybutadiene is present in amounts from 70 to 80grams per liter of said initially liquid material; and said crosslinkingagent comprises isocyanate and is present in amounts from 8 to 10 gramsper liter of said material.
 5. Apparatus in accordance with claim 4wherein said hydroxyl-terminated polybutadiene has a hydroxylfunctionality between 2.2 and 2.4 and a hydroxyl content between 0.75and 0.90 equivalents per kilogram, and said oil contains at least 90weight percent of aromatic molecules.